I2c slave implementation

examples/board_i2cslave/Makefile

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+# 
+# 	Copyright 2008-2012 Michel Pollet <buserror@gmail.com>
+#
+#	This file is part of simavr.
+#
+#	simavr is free software: you can redistribute it and/or modify
+#	it under the terms of the GNU General Public License as published by
+#	the Free Software Foundation, either version 3 of the License, or
+#	(at your option) any later version.
+#
+#	simavr is distributed in the hope that it will be useful,
+#	but WITHOUT ANY WARRANTY; without even the implied warranty of
+#	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#	GNU General Public License for more details.
+#
+#	You should have received a copy of the GNU General Public License
+#	along with simavr.  If not, see <http://www.gnu.org/licenses/>.
+
+target=	i2ctest
+firm_src = ${wildcard at*${board}.c}
+firmware = ${firm_src:.c=.axf}
+simavr = ../..
+
+IPATH = .
+IPATH += ${simavr}/examples/shared
+IPATH += ${simavr}/examples/parts
+IPATH += ${simavr}/include
+IPATH += ${simavr}/simavr/sim
+
+VPATH = .
+VPATH += ${simavr}/examples/shared
+VPATH += ${simavr}/examples/parts
+
+
+all: obj ${firmware} ${target} 
+
+include ${simavr}/Makefile.common
+
+atmega1280_${target}.axf: atmega1280_${target}.c twimaster.c
+atmega1280_${target}.axf: ${simavr}/examples/shared/avr_twi_master.c
+atmega1280_${target}.axf: ${simavr}/examples/shared/avr_twi_master.h
+
+board = ${OBJ}/${target}.elf
+
+${board} : ${OBJ}/${target}.o
+${board} : ${OBJ}/i2c_eeprom.o
+
+${target}: ${board}
+	@echo $@ done
+
+clean: clean-${OBJ}
+	rm -rf *.hex *.a *.axf ${target} *.vcd .*.swo .*.swp .*.swm .*.swn

examples/board_i2cslave/README

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+
+This contains a sample program to demonstrate the use of simavr
+using 'custom' code, and own "peripherals". It shows how it is
+possible to "hook" code to the AVR pins, and also how to make
+"peripherals" and also hook them up to AVR pins.
+
+This demo demonstrate how to write a i2c/twi "peripheral" and hook it to
+an AVR, and then run a firmware that behaves as a TWI "slave" to talk to it.
+
+The code uses a generic i2c "eeprom" were the AVR writes some bytes,
+then read them again. The AVR code is based on the Atmel reference
+implementation, with quite a few changes to make it more functional.
+
+Thid "board" doesn't use opengl, the eeprom will display what the
+transactions are.

examples/board_i2cslave/atmega328p_i2cslave.c

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+/*
+        atmega48_i2ctest.c
+
+        Copyright 2021 Sebastian Koschmieder <sep@seplog.org>
+
+        This file is part of simavr.
+
+        simavr is free software: you can redistribute it and/or modify
+        it under the terms of the GNU General Public License as published by
+        the Free Software Foundation, either version 3 of the License, or
+        (at your option) any later version.
+
+        simavr is distributed in the hope that it will be useful,
+        but WITHOUT ANY WARRANTY; without even the implied warranty of
+        MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+        GNU General Public License for more details.
+
+        You should have received a copy of the GNU General Public License
+        along with simavr.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <stdlib.h>
+#include <string.h>
+
+#include <avr/interrupt.h>
+#include <avr/io.h>
+#include <avr/sleep.h>
+#include <util/twi.h>
+
+// for linker, emulator, and programmer's sake
+#include "avr_mcu_section.h"
+AVR_MCU(F_CPU, "atmega328p");
+
+#include <stdio.h>
+
+void __attribute__((section(".init8"), naked)) initTWI(void) {
+  TWAR = (0x42 << 1);
+  TWAMR = 0x7F << 1;
+  TWCR = (1 << TWEA) | (1 << TWEN);
+}
+
+int twi_getState(void) {
+  while ((TWCR & (1 << TWINT)) == 0)
+    ;
+  return TWSR & 0xF8;
+}
+
+static inline void twi_ack(void) { TWCR = (1 << TWEN) | (1 << TWINT) | (1 << TWEA); }
+static inline void twi_nack(void) { TWCR = (1 << TWEN) |  (1 << TWINT); }
+
+static const __flash char msg[] = "Hello AVR!";
+static char buffer[ 128 ];
+static int index;
+
+int twi_receive( char *buffer, size_t size ) {
+  if (twi_getState() != TW_SR_SLA_ACK) {
+    abort();
+  }
+
+  index = 0;
+  twi_ack();
+
+  if(twi_getState() != TW_SR_DATA_ACK) {
+    abort();
+  }
+  index = TWDR;
+  int start = index;
+  twi_ack();
+
+  uint8_t state;
+  while( ( state = twi_getState() ) == TW_SR_DATA_ACK ) {
+    buffer[index++] = TWDR;
+    if( ( index + 1 ) < size ) {
+      twi_ack();
+    }
+    else {
+      twi_nack();
+    }
+  }
+
+  if( state != TW_SR_STOP ) {
+    abort();
+  }
+
+  TWCR = (1 << TWEN) | (1 << TWINT) | (1 << TWEA) | (1 << TWSTO);
+
+  return start;
+}
+
+int twi_send( char *buffer, size_t size ) {
+  if (twi_getState() != TW_SR_SLA_ACK) {
+    abort();
+  }
+
+  index = 0;
+  twi_ack();
+
+  if(twi_getState() != TW_SR_DATA_ACK) {
+    abort();
+  }
+  index = TWDR;
+  int start = index;
+  twi_ack();
+
+  uint8_t state;
+
+  if( ( state = twi_getState() ) == TW_ST_SLA_ACK ) {
+    TWDR = buffer[index++];
+    if( ( index + 1 ) < size ) {
+      twi_ack();
+    }
+    else {
+      twi_nack();
+    }
+  }
+
+  while( ( state = twi_getState() ) == TW_ST_DATA_ACK ) {
+    TWDR = buffer[index++];
+    if( ( index + 1 ) < size ) {
+      twi_ack();
+    }
+    else {
+      twi_nack();
+    }
+  }
+
+  if( state != TW_ST_DATA_NACK ) {
+    abort();
+  }
+
+  TWCR = (1 << TWEN) | (1 << TWINT) | (1 << TWEA) | (1 << TWSTO);
+  return start;
+}
+
+int main() {
+
+  memset(&buffer[0], 0xFF, sizeof(buffer));
+
+  int start = twi_receive( &buffer[0], sizeof(buffer) );
+
+  for( int i = 0; i < sizeof( msg ); i++ ) {
+    if( buffer[start+i] != msg[i] ) {
+      abort();
+    }
+  }
+
+  start = twi_send( &buffer[0], sizeof(buffer) );
+
+  cli();
+  sleep_mode();
+}